Feat: add support for multi-column PDF parsing (#10475)

### What problem does this PR solve?

Add support for multi-columns PDF parsing. #9878, #9919.

Two-column sample:
<img width="1885" height="1020" alt="image"
src="https://github.com/user-attachments/assets/0270c028-2db8-4ca6-a4b7-cd5830882d28"
/>

Three-column sample: 
<img width="1881" height="992" alt="image"
src="https://github.com/user-attachments/assets/9ee88844-d5b1-4927-9e4e-3bd810d6e03a"
/>

Single-column sample:
<img width="1883" height="1042" alt="image"
src="https://github.com/user-attachments/assets/e93d3d18-43c3-4067-b5fa-e454ed0ab093"
/>



### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)
- [x] New Feature (non-breaking change which adds functionality)

rag/app/naive.py

@@ -328,7 +328,7 @@ class Pdf(PdfParser):
         callback(0.65, "Table analysis ({:.2f}s)".format(timer() - start))
 
         start = timer()
-        self._text_merge()
+        self._text_merge(zoomin=zoomin)
         callback(0.67, "Text merged ({:.2f}s)".format(timer() - start))
 
         if separate_tables_figures:
@@ -340,6 +340,7 @@ class Pdf(PdfParser):
             tbls = self._extract_table_figure(True, zoomin, True, True)
             self._naive_vertical_merge()
             self._concat_downward()
+            self._final_reading_order_merge()
             # self._filter_forpages()
             logging.info("layouts cost: {}s".format(timer() - first_start))
             return [(b["text"], self._line_tag(b, zoomin)) for b in self.boxes], tbls